This issue can have two causes:
1.) The DLL that is loaded into MATLAB is a 32-bit DLL but it is used a MATLAB 64-bit version, see the following MATLAB Answers thread for more information,
In such a case the resolution of the issue would involve installing and using a 32-bit version of MATLAB.
2.) The DLL that is loaded in MATLAB through the COM interface does not have the particular class registered.
If the third-party application is run as an out-of-process ActiveX server, then the issue most likely lies in point 2.). To resolve this issue, the developer of the third-party program needs to register the class in the generated DLL, before one can access it through MATLAB via the COM interface.